1. Field of the Invention
The present invention is related to integrated circuit design techniques, more particularly to a voltage regulator with a current limiting circuit having low quiescent current.
2. Description of Related Art
With more uses of portable electronic devices, engineers start to pay more and more attention to the design of standby power consumption of the portable electronic devices. The standby power consumption directly influences an operating time of the portable electronic devices. Battery capacity of the portable electronic devices is very limited, so it needs to reduce quiescent currents of various electronic components of the portable electronic device as much as possible. Hence, various power management integrated circuits are used in the portable electronic devices, such as low dropout voltage regulators or DC-DC converters etc., to continuously reduce the quiescent current during light loading.
A low dropout voltage regulator is taken as an example for illustration hereafter. The voltage regulator comprises a reference voltage source, an error amplifier, an output pass circuit, a sampling resistor and a bypass circuit. The error amplifier may be a comparator. A reference voltage provided by the reference voltage source is coupled to an inverse input of the comparator. A sampling voltage obtained by sampling an output voltage of the output pass circuit via the sampling resistor is coupled to a non-inverse of the comparator, thereby a negative feedback loop is formed. A difference between the reference voltage and the sampling voltage is amplified by the error amplifier to control the output pass circuit until the output voltage of the output pass circuit goes to stabilization. The output pass circuit may be implemented by a bipolar transistor or a Metal-Oxide Semiconductor Field Effect Transistor (MOSFET).
Additionally, it is necessary for the low dropout voltage regulator or the DC-DC converter to employ a current protection circuit, also referred as a current limiting circuit, which can effectively limit the current passing through the output pass circuit of the low dropout voltage regulator or the DC-DC converter during short circuit or overload. However, the conventional current limiting circuit may have a great quiescent current when the power management IC, such as the low dropout voltage regulator or the DC-DC converter, is under no load condition.
Referring to FIG. 1, a circuit diagram shows a prior art low dropout voltage regulator 100 with a current limiting circuit, either the current limiting circuit or a current source 18 therein may introduce a great quiescent current.
Thus, improved techniques for the current limiting circuit are desired to overcome at least the above disadvantages.